Archive for the ‘touring equipment’ Category

the bridge pickup improved

A couple of months ago, I tried making a Cortado-based bridge pickup for the octave mandolin. It worked okay – better than the ad-hoc clamp arrangement I’d bodged together for last January’s Conflikt show, but not what I’d hoped. It was a lot more stable, but still needed lots of equalisation help.

I’ve built a new one, with a new design! It’s much better. Here’s an mp3 of the previous design alternated with the new design, on octave mandolin – no eq of any kind, no effects, just raw output from the old design vs. the new. (Old design is first.)

While working with the previous attempts, I’d figured out what really improved things was the right kind of pressure on the piezo disc itself. My thumb was pretty optimal, but you can’t exactly do that and play at the same time. The clamp wasn’t bad, but it was slippery and awkward and actually came off on me during rehearsal, so I didn’t trust it. Most piezo-style pickups live under the bridge of an instrument, but you can’t do that the usual way with this one, it’d be destroyed by the pressure.

So I went about trying to fix that.

First was to take the bridge plate and add a wide, flat channel – one wide enough specifically to contain the entirety of the Cortado piezo element. I made it by wrapping sandpaper around a flat piece of metal, and scrubbing back and forth to excavate out the wood I needed removed.

This is actually a new bridge plate.
But it’s made of the same material, so no real diff.

You need to sand away enough wood to make room for the piezo and all the tape wrappings, and some extra. But you do not need to sand away enough for the wires soldered to the disc – you want to avoid those entirely.

Keep sanding away wood until the bridge slides freely over both the new channel and the piezo, like so:

What this makes is basically a wide clamping chamber around the pickup element itself. It doesn’t do any clamping yet; it just creates a space for it. At this stage, in fact, if you hook it up and try it, there’ll no change in sound from the previous version.

(In fact, the “old design” recording I used in the sample is actually this version at this point in the process. I verified that it sounded exactly the same as the previous version, as predicted, which means I’d re-established the old baseline. Important for science!)

But now, of course, I have a clamping chamber! We just need something to apply pressure.

So what’s our clamp? Pieces of paper. Post-it notes, to be specific, just because they were handy. The right number of sheets in this exact case turned out to be four.

Five also worked, and did not feel like too much pressure inserting the papers under the bridge. But it did sound like a bit much compression, tonally, so I went back to four.

(Here’s that sample track again, alternating old design and new, old first.)

The beauty of this is that since it takes several thicknesses of paper, and since that paper be changed out without taking apart the pickup, you can use any number you like. You could even adjust the tone on the fly.

Interestingly, the pickup didn’t even get quieter with more paper. I’d worried about that, but didn’t need to. In fact, adding more sheets made it louder, meaning that the pressure is not so much “damping down treble” as it is pulling up bass. Which, in turn, makes me wonder if it’s not so much “resonating better” as moving the zero/no-vibration point of the crystals’ charge state from all-electrons-in or all-electrons out (doesn’t matter which) to a more middle-range position, which…

…hm. Actually, that’s interesting. No, that’s really interesting. That would explain why the pickup got louder with more clamping, rather than muffled or…

…huh. This is an hypothesis. If I’m right, I can make my next crystal mic substantially more modern sounding, by enclosing the piezo in a small clamping chamber, which is, like this, attached to the resonating disc of the microphone, and possibly…

…possibly I should take my SRMD meds now or I’m going to be up until 5am next Thursday playing with crystals and possibly taking over the moon again, aren’t I? Yeah. I am. Okay. BRB.

So. Yeah! I’m super-pleased with this result. I’m also thinking that maybe this could be used on other items that have flat surfaces which need pickups – like, a piano, maybe – and instead of the bridge, as here, you use a weighted flat bar of some sort across the pickup plate to create the clamping chamber. Then you’re off with tonal control via paper again. I have no need for this functionality at the moment, but it strikes me as legitimate nonetheless.

And most importantly for me, I now have a much more conventional DIY pickup for the octave mandolin. Here y’go, doc – just plug ‘er in, and we’re off.

Much better.

experiments in DIY pickups, part two

A couple of months ago, I built a Zeppelin Labs cortado instrument pickup from a kit. I ended up using it on stage, attached to my octave mandolin with a plastic clamp.

It worked well enough, but needed a fair bit of equalisation, plus there was that whole “giant blue clamp” thing. It also had a fairly metallic sound, which is either good or bad, depending upon what you’re looking for. In this case, that was good, but that’s not always true.

So I had an idea – I’d try to work around all of the above by building a second pickup, with this one’s piezo disc affixed to a hardwood plate. To do that, of course, I’d need a new bridge for the octoman, just so the strings wouldn’t be pushed super-high up in the air by the addition of the plate. Fortunately, those are cheap on eBay.

And now I’ve built it. To wit:

It’s Alive

Installed on the octave mandolin

I was hoping for something akin to the sound I got with the clamp… no. That’s not true. That still had issues. No, I was hoping for the held-down-by-hand sound, the best sound I could get with version one, which I could get no other way, and thus no useful way, since I kind of need my hands to play the instrument. They’re too busy to also press the pickup plate onto the face of the octoman. Hence: this approach.

The result… it’s better. But I didn’t quite get there. I didn’t even get the amount of bass pickup I did with the clamp solution on the first pickup. But what I did get was a more naturalistic sound, and more importantly, a better curve of sound, one that I could get into the area of live sound with a simple single-point parametric equalisation curve.

That curve looks like this. Simple, clean, ignore the red line (unrelated) and the small jagged spikes (room noise):

Simple… but kind of a lot. (+19db peak)

Here’s the riff from “Thirteen,” played back with that single curve added. If you want something in more normal octave mandolin tuning, here’s a short bit of Pirate Bill, played with medium force. I find this instrument really uncomfortable to play in GDAE, so forgive the shakiness. I really don’t like the way the fretboard works on this thing.) No other processing, including compression; those are just the raw recordings plus that one EQ point added.

It’s not where I hoped to get, but it’s pretty good – particularly for live. I think that the clamp – and my fingertip, holding the pickup down directly – has been damping down the high end, the higher frequency sounds. The pickup still needs EQ when I do that, just less, and this has the advantage of being… well, it’s a large shift, but a simple one. That has major advantages in real life.

Part of the problem is, honestly, that these little discs are really sensitive, which is good, but that sensitivity starts falling off pretty hard below 300hz. They still pick up the sound, but not nearly as strongly. That in turn implies that the dampening approach might be best, but that has its own problems, even if the idea of building in some sort of adjustable pressure device is kind of hilarious. And… maybe worth trying anyway, actually. Hm.

Regardless, given that the amount of LOUD in this kit is very goddamn high – it’s very sensitive, with a nice low noise floor – I’m wondering if a low-pass filter in the pickup circuit hardware itself would be the best approach. Sure, you’d lose some signal, but it currently needs so little amplification that a subtractive approach might just be… fine.

After making those recordings, I added some tape to hold down the cord – wouldn’t want to yank that cable off the kit, now would we:

I’ve got one more of these kits, and I want to build a boundary mic with it. And I’m wondering whether I can add such a filter directly onboard. That might be all it needs.

who was lakeside engineering?

I guess I lied, there is one more stage monitor speaker post, sort of.

I’m still kind of curious about who “Lakeside Engineering, Seattle, Wash.” might have been. Here’s a scan of the logo, off the better old patch panel, now removed. (The worse one had been partly painted over. I’ve saved both, I might add. No good reason, really, but it’s not like they’re big.)

I’ve cleaned up the scan and made the black background solid black again, but I haven’t really altered anything in the logo itself. I even left the scratches, and missed spots in the original silkscreen.

If you know anybody who might know who Lakeside Engineering was, pass this along. I’m mostly just curious, and kind of feel a little like sending someone down memory lane. And if they want to see some of their gear put back into order, just point them at the compilation post.

I’ve re-badged the speakers, by the way:

Because hey – why not?

i can still paint during blackouts

I can paint during blackouts, I can play with handheld sequencers during blackouts.

Basically, I got bored and started making theme songs for tacky game shows of the 1970s which never existed. None of these were good, of course, but this one was probably the least bad – I figure it’s circa 1977, a slot-machine celebrity-trivia-themed game show involving a lot of guest appearances by Jo Anne Worley and Phyllis Diller.

Oooh, bad luck there. <sad horn> Next contestant, pull that bandit!

Oh right, painting. Yeah, this is probably the last speaker post. I finally connected them up to my Samson amp to test the old-style connectivity, and the little Class T amps I added in are definitely better. Okay, the Samson has more bass, that’s fair. But wow, these miniboard amps are a lot more precise and focused in every other way.

And after the power went, out I painted ’em. These pictures aren’t 100% before-and-after, because I’d already cleaned them up a lot before taking the “before” shots. Yeah. Literal caked dirt filling the foam rings around the woofers. Sound quality aside, just consider that for a minute.

Yeah! This is what I meant on Twitter about looking like they belonged on a stage. Go you, paint!

This post is part of a series on restoring infamous vintage stage monitors. Spoiler: they made good, in the end.

the saga of the infamously terrible stage monitors made good

John Seghers, local sound guy, gave me a set of locally-infamous and astoundingly terrible stage monitors. I mean, seriously, they just hurt to listen to; musicians would cringe when they saw them on stage.

They’d been through a lot of bands by the time they reached me, and came with an amp I was also being given. They were, in fact, more or less the price of the amp – if I wanted that, I had to take these wretched things too, just so John didn’t have to haul them to the dump.

And upon testing, they were indeed hilariously terrible. They totally lived down to their reputation. There was dirt caked in the speaker foam, and they were filled with fibreglass insulation and in one case quite literally a small dead animal. I was looking at a parody of bad stage gear.

But that is not the story. The actual story is how it turned out they were secretly – very secretly – great, just… buried, and muddled beyond all recognition.

They’re back now; for the first time in literally decades, they sound really, genuinely good. But it was a long way home. This is how we got there.

The original back panel – anybody ever heard of this crew?

i have basically implemented a soviet joke

I have basically implemented a very old joke from Poland about Soviet technology:

A Pole waiting at a railroad platform in Moscow wants to know the time. He sees a man approaching him carrying two large, heavy suitcases, and asks the fellow if he what time it is.

“Certainly,” says the Russian, setting down the two bags and looking at his wrist. “It is 11:43 and 17 seconds. The date is Feb. 13, the moon is nearing its full phase and the atmospheric pressure stands at 992 hectopascals and is rising.”

The Polish visitor is astounded, and asks if the watch that provides all this information is Japanese. “Not at all,” says the man, indignantly. “It is a product of the latest in Soviet technology!”

“Well!” says the Pole, impressed. “That is wonderful, you are to be congratulated!”

“Thank you,” the Russian answers, straining to pick up the suitcases as the train arrives. “But I’ll admit, these batteries are still a little heavy.”

To wit, these self-powered iPod speakers:

iPhone compatible

Okay, they are obviously not actually generally for use as iPod speakers. They’re the stage monitors I’ve been working on occasionally for the last few months, but they are now both rebuilt to be self-powered! They have 50-watt Class T amplifiers built-in, as well as power converters for line voltage. I knew all those spare computer power cables would come in handy eventually.

I did not, despite temptation, add Bluetooth. But I could.

Now it’s time for some burn-in. Hopefully, I’m almost done! 😀

eta: Well, hell, the new amp’s channel 1 got noisy after a couple of hours and stayed that way. channel 2 is clean so far – all of these boards are dual-channel – let’s hope it’s good.

eta2: So far, so good: WE’RE BURNINATING THE AMPLIFY (video with sound)

eta3: With this speaker, they apparently originally tried to put the panel right behind the tweeter horn, where nothing could be inserted. Then they moved it and patched the hole with plywood. I just made it one big panel, with a big blank area.


This post is part of a series on restoring infamous vintage stage monitors. Spoiler: they made good, in the end.

it has now occurred to me that I may be suffering from science-related memetic disorder

I realised this morning that I could totally add Bluetooth to this monster of a stage monitor I’ve been rebuilding and upgrading. I’ve made it self-powered and compliant to modern specs, why stop there? It’s portable! It even has a handle!

48 pounds! Two pounds less than a standard bag of concrete! PORTABLE!

I mean, okay, sure, I’d need a second one to deliver full stereo, but I could do that because I have two of them and could put on another jack to share channel two over to the second speaker and and and IT COULD WORK!

Someone please put a towel over my head.

This post is part of a series on restoring infamous vintage stage monitors. Spoiler: they made good, in the end.


So yesterday I mentioned that the first stage monitor had some physical issues, and what the big one turned out to be is that one of the XLR sockets on the new control panel extended too far into the cabinet, and rattled against the tweeter driver.

That’s really annoying and generally not good, but fortunately I have some shallower ones handy, and hey, the hole is about the same size, and hey, the screw mounts are about the same distance apart, this should be perfect!

Not as much.

Now, this has exactly zero functionality impact. It really doesn’t. But wow, it’s annoying. Not quite annoying enough to make an entirely new Delrin panel and unsolder and reconnect every wire, but still. Annoying.

Anyway, it’s totally working now. I have successfully upgraded this antique to modern specs. It’s not quite like taking an old grandfather clock and setting it up to run network time protocol, but… actually it’s a lot like that. Go Team Pointless! Except it’s not, it’s actually useful now.

The link is to video made on a phone of an iPod playing through the speaker by direct cable connection, no other parts. Yes, it’s also now the heaviest portable – luggable – iPod external speaker ever.

Tho’ even with the wonky socket, the panel still looks decent labelled.

Made and Designed in Cascadia with Chinese, Canadian, American, and Cascadian Parts.

I’ll open it back up to tie down some cables, but other than a little more testing, this one’s done. Speaker two is next. Probably won’t post many photos, it’d just be reruns. But if I learn something I’ll post about that.

This post is part of a series on restoring infamous vintage stage monitors. Spoiler: they made good, in the end.

a few quick pictures and a name

As per Twitter last night, installed, it’s looking a little less like Star Trek and a little more like K-9. So I’m calling it dB-90.

There are a few more physical issues to work out (something rattles when loud), but it’s getting there. Here’s a video not loud, recorded after everybody else was asleep.


This post is part of a series on restoring infamous vintage stage monitors. Spoiler: they made good, in the end.

more and more like a star trek panel

So following up on materials suggestions made in response to the previous post on this stage monitor project, I’ve been playing with Delrin (acetal copolymer), a long-polymer-chain plastic.

It looks even more old-Star-Trek than the diagrammes I made. Seriously, I’m wondering if they made the bridge consoles out of this stuff. Cut a bunch of holes for buttons into it and you’re off.

Which is exactly what we’re about to do. But first, lj:tereshkova2001 asked if I would report back about how this plastic works as a material. Since that’s pretty hard-core geekery, I’m including that down at the bottom of this post, and talking about the panel assembly first.

So after I cut off my new panel backing from the rest of the sheet I’d bought, I decided the easiest and best way to place all these holes would be to adhere the printed scale diagramme to the plastic itself, and just drill through the paper at appropriate points.

Since movable spray fixative doesn’t seem to be a thing anymore, I came up with an alternative plan of two layers of tape – one single-sided, one double-sided. The single-sided layer is packing tape (of which I have lots), applied to the panel:

One of the reasons I didn’t just use double-sided tape in a single layer is that stuff is really hard to remove, so if I tape it to tape that’s easier to remove, I don’t have to fight that battle. Also, the packing tape is wider, meaning the holes cut in the tape don’t break any single entire length of tape, which means I always have a section of “handle” when pulling the tape up once we’re done.

Anyway, then the double-sided tape goes on the back of the cutting diagramme:

And that gets us to the third reason for two layers of tape: I had to position the diagramme on the panel so the hole guides are in the right place. You can’t really draw on Delrin, or on double-sided tape, but you can certainly use your pink glitter gel pen on ordinary packing tape just fine:

And now you know exactly where to position your cutting guide/diagramme on the panel.



As I was warned, this material really likes climbing the drill bit. That’s true for any plastic, and this isn’t worse, but it isn’t better, either. Fortunately, that wasn’t doing any actual damage. This is what one of the holes looked like:

Along with an insert test, which showed that yep, this seems to be working fine. I drilled out the rest of the holes, and peeled off all the tape. Having tried this before with double-sided tape only, adding the packing tape layer made this much easier.

Eventually I got most of the sockets and switches and such in place. A few of them needed separate bolts to hold them onto the board. Drilling those holes also involved tape for position control, but in a slightly different way. Again, you can just drill through the tape:

As of writing this, I have all the components integrated into the panel. I’m really pretty happy with it. There are a couple of little scratches which aren’t my favourite things in the world, but it’s not like anybody will notice them, ever.

As you can see, I have started wiring the thing. Green light means “plugged in,” red light means “power switch is ON.” Those are neon and I’m a little worried about noise from that – it’s not supposed to be an issue, but No Trust I, so I’m probably going to wrap the backs of those in copper shielding. If I have to, I can cut them out entirely and have no harm done.

And besides, it looks pretty cool.

I still need to drill attachment screw holes around the outer edge of the panel – which I kind of forgot about until just now, oops – but that won’t break anything. Then it’s wiring harness time!

I hope this keeps working out. See, what I’d really like to do is be able to move up to a modern iPad-driven sound system, but all of those use and expect self-powered speakers. If I can make these passive monitors into self-powered and it actually works? That’d let me actually move my gear into this century. Which would be really nice.

Anyway, that’s where the project stands right now. Hopefully I’ll get to work on it more tonight and have another update soon.


For the record, I’m using the basic Delrin formulation (no glass particles added as a hardener, etc), at 3/16th” thickness.

absynthe77’s comment that it works kind of like a very soft aluminium kind of stands up. It’s not exactly like that – you can melt this with a cutting wheel in ways you can’t melt aluminium, for example – but I see what they mean.

The aforementioned melting is minimal and not bothersome. It doesn’t clump up into a paste like acrylic plastics do, which is much nicer, and it doesn’t foul your tools, which is critical. You can cut it with an edge-grinding Dremel bit and it doesn’t get goopy and weird; it flakes off in manageable pieces, instead. But it’s still soft enough to cut with a basic Dremel cutting wheel and I haven’t accumulated much wear yet.

Here’s an edge cut made that way:

Note the circular-saw-like cut pattern; it didn’t melt the plastic away, it cut.

Unlike acrylic, Delrin does not score-and-snap. I gave it quite the depth of cut and got absolutely nowhere trying it. I even gave it another go after getting out a cutting wheel, just to see if I hadn’t scored enough, but no, it just wasn’t having any of it – not until I was almost entirely through the sheet. So while it has some flex, it’s very strong against snapping and cracking.

In some ways, working with it kind of reminds me of linoleum block print cutting, only a much harder material. With a Dremel cutting ball, for example, you can scoop bits of it out, almost exactly like linoleum block cutting. That’s pretty nice, and is how I made the square holes I needed – well, that and an xacto knife and file for finish work. Most of it was just scooping out plastic with the Dremel.

I haven’t worked with many plastics, and when I have, I generally haven’t enjoyed it, but this… this is fine. Fouling isn’t an issue, it doesn’t send sparks like metal so you don’t have to worry about shop-vac fires and can run the vacuum the entire time, I didn’t really seem to be able to overheat it in a meaningful way.

If there’s a downside, it’s that it does scratch like plastic, and more easily than aluminium. So you’ll need to take some care with that. It’s not look-at-it-funny-and-it-scratches soft, but a stray screwdriver would definitely leave a mark.

So, yeah. Definitely something I’m glad to be able to add to the toolkit. At least, so far.

eta: I’ve discovered the old speaker-level inputs used by both speaker and amp are an obsolete cable connection standard. I’m upgrading the speakers to self-powered, but I want to maintain the speaker-level-input functionality too. Do I re-implement the old standard? I mean I guess so, but. Ugh.

eta2: It was, for the record, a stupid standard.

This post is part of a series on restoring infamous vintage stage monitors. Spoiler: they made good, in the end.

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